Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology characterized by chronic inflammation in multiple joints. It is estimated that the prevalence of RA is 0.8%, making it one of the most common autoimmune diseases and the most common cause of inflammatory arthritis. In a significant fraction of patients, the chronic arthritis leads to destruction of the joint cartilage and surrounding joint structures. RA is a major cause of disability and morbidity.